#include <fstream>
#include <vector>
#include <stack>
#include <unordered_set>
using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

using US  = unordered_multiset<int>;
using VUS = vector<US>;
using VI = vector<int>;

int n;
VUS G;
VI c;

void citesteGraf();
inline void detCiclu(int x);
bool esteEulerian();

int main() {
	citesteGraf();
	if ( !esteEulerian() ) {
		fout << -1;
	} else {
		detCiclu(1);
		
		for (size_t i = 0; i < c.size() - 1; ++i)
			fout << c[i] << ' ';
	}
}

int x, y, m;

inline void detCiclu(int x) {
	
	stack<int> stk;
	stk.push(x); 
	
	while (!stk.empty()) {
		x = stk.top();
		if (G[x].empty()) {
			stk.pop();
			c.emplace_back(x);	
		} else {	
			auto it = G[x].begin(); y = *it;
			G[x].erase(it);   
			it = G[y].find(x);
			if (it != G[y].end())
				G[y].erase(it); 
			stk.push(y); 
		}
	}
}

bool esteEulerian() {
	for (auto ms : G)
		if (ms.size() & 1)
			return false;
	return true;
}

void citesteGraf() {
	fin >> n >> m;
	G = VUS(n + 1);
	while (m--) {
		fin >> x >> y;
		G[x].emplace(y);
		G[y].emplace(x); 
	}
}